Buggy code:
@ Mod ( modid = RFTools . MODID , name = "RFTools" , dependencies = ( ( ( "required-after:Forge@[" + ( RFTools . MIN_FORGE_VER ) ) + ",);required-after:CoFHCore@[" ) + ( RFTools . MIN_COFHCORE_VER ) ) + ",)" , version = RFTools . VERSION ) public class RFTools { public static final String MODID = "rftools" ; public static final String VERSION = "2.55" ; public static final String MIN_FORGE_VER = "10.13.0.1230" ; public static final String MIN_COFHCORE_VER = "1.7.10R3.0.0B9" ; @ SidedProxy ( clientSide = "com.mcjty.rftools.ClientProxy" , serverSide = "com.mcjty.rftools.ServerProxy" ) public static CommonProxy proxy ; @ Mod . Instance ( "rftools" ) public static RFTools instance ; public boolean enderio = false ; public Logger logger ; public static EnumMap < Side , FMLEmbeddedChannel > channels ; private static int modGuiIndex = 0 ; public static boolean debugMode = false ; public ClientInfo clientInfo = new ClientInfo ( ) ; public static CreativeTabs tabRfTools = new CreativeTabs ( "RfTools" ) { @ Override @ SideOnly ( Side . CLIENT ) public Item getTabIconItem ( ) { } } ; public static CreativeTabs tabRfToolsDimlets = new CreativeTabs ( "RfToolsDimlets" ) { @ Override @ SideOnly ( Side . CLIENT ) public Item getTabIconItem ( ) { } } ; public static final String SHIFT_MESSAGE = "<Press<seq2seq4repair_space>Shift>" ; public static final int GUI_LIST_BLOCKS = ( RFTools . modGuiIndex ) ++ ; public static final int GUI_RF_MONITOR = ( RFTools . modGuiIndex ) ++ ; public static final int GUI_LIQUID_MONITOR = ( RFTools . modGuiIndex ) ++ ; public static final int GUI_CRAFTER = ( RFTools . modGuiIndex ) ++ ; public static final int GUI_STORAGE_SCANNER = ( RFTools . modGuiIndex ) ++ ; public static final int GUI_RELAY = ( RFTools . modGuiIndex ) ++ ; public static final int GUI_MATTER_TRANSMITTER = ( RFTools . modGuiIndex ) ++ ; public static final int GUI_MATTER_RECEIVER = ( RFTools . modGuiIndex ) ++ ; public static final int GUI_DIALING_DEVICE = ( RFTools . modGuiIndex ) ++ ; public static final int GUI_TELEPORTPROBE = ( RFTools . modGuiIndex ) ++ ; public static final int GUI_MANUAL_MAIN = ( RFTools . modGuiIndex ) ++ ; public static final int GUI_MANUAL_DIMENSION = ( RFTools . modGuiIndex ) ++ ; public static final int GUI_ENDERGENIC = ( RFTools . modGuiIndex ) ++ ; public static final int GUI_SEQUENCER = ( RFTools . modGuiIndex ) ++ ; public static final int GUI_COUNTER = ( RFTools . modGuiIndex ) ++ ; public static final int GUI_PEARL_INJECTOR = ( RFTools . modGuiIndex ) ++ ; public static final int GUI_TIMER = ( RFTools . modGuiIndex ) ++ ; public static final int GUI_ENDERMONITOR = ( RFTools . modGuiIndex ) ++ ; public static final int GUI_SHIELD = ( RFTools . modGuiIndex ) ++ ; public static final int GUI_DEVELOPERS_DELIGHT = ( RFTools . modGuiIndex ) ++ ; public static final int GUI_DIMLET_RESEARCHER = ( RFTools . modGuiIndex ) ++ ; public static final int GUI_DIMENSION_ENSCRIBER = ( RFTools . modGuiIndex ) ++ ; public static final int GUI_DIMENSION_BUILDER = ( RFTools . modGuiIndex ) ++ ; public static final int GUI_DIMLET_SCRAMBLER = ( RFTools . modGuiIndex ) ++ ; public static final int GUI_MACHINE_INFUSER = ( RFTools . modGuiIndex ) ++ ; public static final int GUI_DIMENSION_EDITOR = ( RFTools . modGuiIndex ) ++ ; public static final int GUI_ITEMFILTER = ( RFTools . modGuiIndex ) ++ ; public static final int GUI_SCREEN = ( RFTools . modGuiIndex ) ++ ; public static final int GUI_SCREENCONTROLLER = ( RFTools . modGuiIndex ) ++ ; public static final int GUI_DIMLET_WORKBENCH = ( RFTools . modGuiIndex ) ++ ; public static final int GUI_ENVIRONMENTAL_CONTROLLER = ( RFTools . modGuiIndex ) ++ ; public static void logError ( String msg ) { } public static long prevTicks = - 1 ; public static void log ( World world , TileEntity te , String message ) { } public static void log ( String message ) { } public static void logDebug ( String message ) { } @ EventHandler public void preInit ( FMLPreInitializationEvent e ) { } @ EventHandler public void init ( FMLInitializationEvent e ) { } @ EventHandler public void serverLoad ( FMLServerStartingEvent event ) { } @ EventHandler public void serverStarted ( FMLServerStartedEvent event ) { } @ EventHandler public void serverStopped ( FMLServerStoppedEvent event ) { System . out . println ( "######<seq2seq4repair_space>RFTools.serverStopped" ) ; <START_BUG> RfToolsDimensionManager . unregisterDimensions ( ) ; <END_BUG> TeleportDestinations . clearInstance ( ) ; RfToolsDimensionManager . clearInstance ( ) ; DimensionStorage . clearInstance ( ) ; DimletMapping . clearInstance ( ) ; RedstoneChannels . clearInstance ( ) ; } @ EventHandler public void postInit ( FMLPostInitializationEvent e ) { } public static void message ( EntityPlayer player , String message ) { } public static void warn ( EntityPlayer player , String message ) { } }

Fix:
RfToolsDimensionManager . cleanupDimensionInformation ( ) ;